The present invention relates to the technology of attaching edge bands to the surface of workpieces.
More particularly the present invention relates to a method of attaching an edge band to at least one narrow face of an in particular panellike workpiece by jointing, and also to the workpieces obtainable by the method of the invention and to apparatus for carrying cut the method of the invention.
The present invention further relates to the use of a plasma for attaching edge bands to narrow faces of in particular panellike workpieces.
In the prior art there is a multitude of methods known for attaching edge bands to narrow faces of panellike workpieces.
Edge bands are conventionally attached in a through-travel machine, such as an edging machine, by means of an edge-gluing assembly, to the narrow faces of panellike workpieces. The edge band in question is supplied to this assembly, for example, from a magazine, and a hotmelt adhesive is applied to the narrow face of the workpiece usually immediately prior to the advancement of the edge band to the narrow workpiece face.
This is the method used at the present point in time to provide almost all workpieces with edge bands. The method is cost-effective and is suitable for producing relatively large unit numbers, but carries, with it a multitude of disadvantages. The melting of the hotmelt adhesive is energy-intensive and hence entails considerable cost. For example, up to half an hour elapses until an operating temperature of 150 to 210° C. is reached, and, moreover, energy is needed for the heating of the glue container in order to maintain this temperature. The adhesive is applied by rolling or knife coating to the workpiece, and as a result of this, when using chipboard panels, example, chips or pieces of wood may be torn from the workpiece and may therefore foul the roll or doctor blade, leading to a nonuniform and defective bond. Moreover, as a result of the roll or doctor blade application, the applied adhesive layer acquires a grid formation (i.e., so to speak, a pattern, therefore) and hence has a nonuniform thickness, leading in turn to a nonuniform bond. As a result of this, the bondline also becomes susceptible to the penetration of dirt and moisture, and so the bond is parted again over the course of time. Furthermore, when the adhesive is applied, the amount of adhesive needed is so great that, when the edge band is subsequently pressed against the workpiece, adhesive swells out of the bondline and hence contaminates not only the workpiece but also the processing machine. In order to prevent this, the workplace must be treated with release agents before the beginning of the method, and this is costly and inconvenient. On account of the described disadvantages of this method, a search has been on for some time for alternative possibilities for attaching edge bands to narrow faces of panellike workpieces.
Other methods of the prior art attempt to prevent, these disadvantages by using an edge band already coated with adhesive, where the coating or providing of the edge band with the hotmelt adhesive can be performed before the edge band is advanced to the narrow workpiece face. In this method, the adhesive is heated to a temperature above its melting temperature, and is held at that temperature. The hotmelt adhesive can be heated using, for example, hot air, infrared radiation or UV radiation, or microwaves. All methods have the disadvantage that the energy transfer to the adhesive is weak and that the heating of the hotmelt adhesive is therefore relatively protracted. These methods are therefore unsuitable for high throughputs or large unit numbers; moreover, the edge band must be very resistant to high temperatures, since all of the methods always entail tab edge band being highly heated as well. As a result of the cooling times that are therefore necessary, the production operation is drawn out even further, and only a very limited selection of materials are suitable for the production of the edge bands.
DE 10 2006 021 171 A1 describes an edge band identified as a cover strip, provided for attachment to a panellike workpiece and composed of an extrudable thermoplastic. In that strip the adhesive layer is applied to the edge band in the form of a hotmelt adhesive, by coextrusion, and accordingly it is necessary, for the purpose of affixing the edge band to the narrow face of the furniture panel in question, for the layer of hotmelt adhesive to be melted again, at least in regions. This is done by means of laser radiation directly in the course of affixing, and for this purpose a laser-compatible or laser-activatable adhesive layer is provided which can be melted or activated with the aid of the laser radiation.
With the laser radiation, the heat transport achieved is indeed more intensive than that possible with infrared radiation or with hot-air irradiation. The use of the laser-assisted coating method in an industrial manufacturing operation on a woodworking machine, however, is accompanied by considerable difficulties: for instance, costly and inconvenient safety measures must be taken in order to protect the operational staff from the laser radiation. The laser radiation must, furthermore, be absorbed by the layer of hotmelt adhesive, and this may be affected by transmission and reflection. The transparency of the hotmelt adhesive material, too, plays a part with regard to the optical depth of penetration, which is influenced by pigment particles and the like. The depth of penetration of the laser and the energy input by the laser must be selected such as on the one hand to provide for rapid heating of the adhesive layer but on the other hand such that the edge band does not suffer any damage due to excessive temperatures. Furthermore, using a laser unit for the outlined purpose is very cost-intensive, and connected with this is the fact that integration into an existing production line involves considerable difficulties. In particular, the operation of the laser unit is relatively energy-intensive and therefore not very economic.